An ergo assist station on an assembly line needs a laser reference line that runs from the 24 VDC control supply, switches with the station logic, and stays aligned through a full shift. Consumer AAA-powered line lasers meet none of these requirements. Two things decide the selection: how much optical power lands on each millimetre of line at the actual work surface, and which laser class that power puts the operator in.
Battery line lasers and engraving catalogs: why the first attempts fail
Three approaches come up first, and each one fails for a physical or categorical reason:
- Consumer battery line lasers. Output drops as cell voltage sags, so the line dims over the shift. There is no enable input, so the PLC cannot switch it with the cycle. Housings and brackets are not built for vibration or continuous duty.
- Searching "laser marker" in automation catalogs. In industrial catalogs, "laser marker" means a marking or engraving system. These are high-power sources in a completely different hazard category. Sensor vendors' laser products are mostly measurement or detection devices, not line projectors. The product category you need is listed as powered laser lines, laser line generators, or laser line projectors. Many of the suppliers are UK or Italy based, so check local distribution and lead time early.
- Hard-wiring the module always-on to 24 V. Diode lifetime is consumed by operating hours and case temperature. An always-on module burns life during breaks and changeovers, and it exposes the operator continuously.
Few powered line lasers offer "two-way" capability, and the term has two meanings. Decide which one you need before you shortlist:
- Status feedback to the PLC. Few modules report their own health. You will have to infer it, for example by monitoring the module's current draw or by adding a photo sensor that looks at the line.
- Lines in two directions. Specify a cross-line optic, or mount two single-line modules.
Line irradiance and working distance: the quantity that decides visibility
A line generator spreads its beam through a fan angle θ. The projected line length at distance d is:
L = 2 · d · tan(θ / 2)The optical power is spread over that length, so power per unit length is roughly P / L. Double the mounting distance, or choose a wider fan, and the line gets proportionally dimmer. Line width also grows with distance unless the optic has a fixed or adjustable focus.
Worked example, with assumed values: d = 1.0 m and θ = 60° give L = 2 × 1.0 × tan 30° ≈ 1.15 m. If the part is only 0.4 m long, roughly two-thirds of the power falls off the part. A narrower fan, or a closer mount, puts more power on the target without moving to a higher laser class.
Wavelength matters as well. At equal power the eye perceives green as brighter than red, which helps under high-bay LED lighting. Green modules are typically more sensitive to temperature, so compare their rated operating range against the conditions at the station.
| Quantity | Limit / decision | Where to read it |
|---|---|---|
| Supply voltage and tolerance | Must cover your 24 VDC bus, including sag and ripple | Module datasheet, electrical section |
| Current draw | Must be below the PLC output point rating, or use an interposing relay | Datasheet; confirm with a clamp or series meter |
| Laser class | Sets the exposure controls at the station | Product label and datasheet |
| Fan angle and focus distance | Sets line length, width and brightness at the work surface | Optic specification; calculate L from the formula above |
| Operating temperature range | Output and lifetime drop as case temperature rises | Datasheet environmental section |
| Enable / modulation input | Allows PLC switching without cycling the supply | Datasheet pinout |
| Ingress rating | Oil mist or coolant on the window dims the line | Datasheet or housing marking |
Laser class and beam path at an operator station
The laser class on the label sets the controls you need, so it is the first safety question to answer. Low-power visible classes depend on the natural aversion response to bright light, which protects only against accidental, brief exposure. Higher classes need engineered controls and a formal review by your site's laser safety function. Pick the lowest class that still gives a visible line, using the power-per-length reasoning above.
Lay out the beam path for the operator's actual posture, including an assist device that raises or tilts the part:
- Mount the projector above the work and aim it downward, so the beam plane never crosses standing or seated eye height.
- Check for specular reflections. Polished, plated or glass parts can redirect the beam toward the operator's face. Sweep the part through its full range of motion with the laser on and watch for stray spots.
- Terminate the beam on the fixture or a matte surface so the line cannot extend past the station into adjacent walkways.
- Apply the class label at the station and record the device in your laser inventory, if your site keeps one.
Wiring a 24 VDC line generator to the station PLC
- Size the supply circuit. Add the module's current draw to the load on the 24 VDC supply that feeds it. Fuse the branch according to the module datasheet.
- Choose how to switch it. If the module has an enable input, keep 24 V applied permanently and drive the enable from a PLC output. This avoids repeated power-up transients on the driver. If it has no enable input, switch the supply directly.
- Check the output rating. Compare the module's current draw with the PLC output point rating. If the draw exceeds it, or is close to it, drive an interposing relay or a solid-state output instead.
- Write the control logic. Turn the laser on only while the station is active, meaning a part is present and the cycle is in progress. Turn it off on idle, break or e-stop.
- Route and protect the cable. Keep the laser cable away from drive output wiring, and add strain relief where the cable crosses a moving assist arm.
Commissioning checks: visibility, thermal drift, switching
- Measure the line at the work surface. Check line length and width against the part tolerance, under production lighting, on every shift's lighting condition.
- Run a thermal soak. Leave the laser on for a full warm-up period, then recheck line position against a fixed reference mark. If the line has moved, the bracket or module has grown thermally. Stiffen the mount or relocate it away from heat sources.
- Verify switching. Toggle the PLC output and confirm the line follows it with no stray emission while the output is off.
- Measure supply current. Record the steady-state draw as a baseline for later diagnostics.
- Check for vibration. Run the line and watch the projected line for jitter caused by conveyors or assist-arm motion.
Recurring faults on powered line lasers and when to escalate
First separate heat faults from logic faults:
- Logic fault. The line is fully absent. Check whether 24 V or the enable signal is missing at the connector.
- Heat fault. 24 V and the enable are both present, but the line dims, flickers or shifts after warm-up. This points to case temperature or diode aging.
Other recurring faults:
- Contaminated window. A dirty window gradually dims the line. Current draw stays normal while visible brightness falls.
- Loose mount. A loose mount lets the line drift after impacts.
- Enclosed housing. A housing without airflow shortens diode life.
Compare the measured current against the commissioning baseline. If the draw has shifted, the problem is electrical. If the draw is unchanged but the line is dimmer, the problem is optical or thermal.
Stop and contact the module manufacturer's official technical support in any of these cases:
- Brightness keeps falling on a clean window at normal case temperature.
- The class label is missing or does not match the datasheet.
- You intend to use the line as part of a safety function.
For class-related exposure questions, involve your site's laser safety authority before the station returns to production.
FAQ
What happens if a laser line generator runs always-on at an assembly station?
The diode wears through its rated life during idle time and heats the housing continuously. Warm modules lose output and alignment drifts. Switch the module's enable input from a PLC output tied to part-present or cycle-active, so it runs only while the operator needs the line.
What happens if the laser line hits a polished or plated part?
The surface can reflect the beam toward the operator's eyes. Sweep the part through its full motion with the laser on, re-aim the projector so any reflections stay below eye height, and terminate the beam on a matte surface.
What happens if I mount the laser line projector farther away to cover a longer part?
Line length grows as L = 2·d·tan(θ/2), and the same optical power spreads over more length, so the line gets dimmer and usually wider. Select a narrower fan angle or a closer mount instead of a higher laser class.